This invention relates to lubrication of refrigeration systems of the closed, hermetically-sealed compression type including halogenated hydrocarbon refrigerant and a lubricant, and more particularly to additives for the prevention of corrosion in such systems.
Sealed refrigerating systems employing as a working fluid a combination of a halogenated hydrocarbon, a refrigerant and a lubricant are subject to wear and corrosion of the metal parts that come in contact with the working fluid. Many combinations of refrigerants and lubricants are subject to a slow deterioration that results in byproducts corrosive to the metal parts and particularly to the ferrous metal components of the compressor. Some system designs, and particularly those in which a less-than-ambient pressure condition exists, are particularly subject to the eventual intrusion of atmospheric oxygen and water. The presence of water and oxygen substantially increases the corrosion of the steel compressor parts, and particularly the steel shell, producing scale and other insoluble materials. These corrosion products are transported into and clog the interstices of heat exchange surfaces. This becomes a major problem in systems employing heat exchange tubing having porous surfaces, in as much as the porosity of these surfaces is rapidly reduced, resulting in a very substantial loss in efficiency.
A variety of approaches have been used to reduce such problems. Improved lubricants having better stability and complexity with refrigerants have been developed, as shown for example in U.S. Pat. Nos. 3,878,112 and 4,046,533. Additives such as metallodithiophosphates have been added to the working fluid to inhibit the interaction between the refrigerant and hydrocarbon lubricants, as shown in U.S. Pat. No. 3,375,197. The transfer of copper from heat exchange surfaces to the steel surfaces of the compressor by the working fluid can also contribute to the corrosion problem, and inhibitors have also been added to the working fluid to reduce such interactions, as shown in U.S. Pat. No. 2,975,137. System driers have also been devised and are widely used to continuously remove moisture from the system.
Corrosion inhibitors for use with aqueous fluids such as are found in adsorption refrigeration systems and the like are widely known. Additives are also widely used in non-aqueous lubricant systems for a great variety of applications, as well as in hydraulic fluids, transmission fluids and the like. In general, such additives are not known for use with halogenated hydrocarbon refrigerants, in as much as most are not soluble in common refrigerants and many promote decomposition of the refrigerant or increase the interaction between refrigerant and lubricant. However, an additive having the requisite solubility in refrigerants and effective in reducing or preventing corrosion under the conditions found in refrigeration systems would be highly useful, particularly for use in sealed systems that operate at less than atmospheric in ambient pressures.